json - composite objects

hi everyone,

i came across a very strange thing. i'm using ajax with jquery. when i
build up the parameters as json i'm creating my data to pass like
this : "{ picture: { photo: this.value, visible: 1, title: '',
description: '' }, bla: '' }" . as far as i know this should be the
right json syntax. when i'm reading the params im my controller i'm
getting this "{"bla"=>"", "id"=>"3", "picture"=>"[object Object]",
"_"=>"1244292346625"}" as a consequence the stringfy_keys method is
not found and i can't process.
does anyone have a clue what i'm missing and give me a hint?

greetings, karl